The present invention relates to an apparatus in the form of an optical emission spectrometer for the analysis, identification or identity testing of metallic materials. The present invention also relates to a method for the optical emission analysis of metallic materials with a spectrometer having at least one arc or spark generator, the spark stand chamber of which is flushed with air.
Spectrometers in general are used for example for the identification of steels. Steels of different compositions cannot be distinguished from one another outwardly. This means that confusion of different materials can arise at any point between production and processing. In the past such confusion has resulted in considerable economic losses. Precautions are therefore needed in the steel-making and processing industries to avoid confusion between materials. Identity testing instruments are used for outgoing products leaving the steelmaker and for incoming products prior to processing in order to verify that the steel is of the expected grade.
The following types of instruments are used for identity testing:                1. Optical emission spectrometers with electric spark discharge in an argon atmosphere (spark OES)        2. Optical emission spectrometers with electric arc discharge in air (arc OES)        3. Energy-dispersive X-ray fluorescence spectrometers (XRF).        
The principle of measurement underlying spark OES and arc OES is for example by Kipsch (Dieter Kipsch, Lichtemissionsspektrometrie, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1974) and Thomsen (Volker B. E. Thomsen, Modern Spectrochemical Analysis of Metals), ASM International, 1996). Information about energy-dispersive X-ray fluorescence spectrometers is provided by Otto (Matthias Otto, Analytische Chemie, Wiley-VCH, Weinheim, N.Y., 2000).
With all three types of instruments, a probe is placed on the workpiece for which the determination is to be made, in other words, measurement is possible without removing a sample.
Spark OES instruments are relatively large (weighing about 25 kg) and additionally require a pressurized gas cylinder of about the same weight containing argon for the discharge atmosphere. A single measurement usually takes longer than 10 s. Before measurement, a flat surface has to be created by grinding the material that is to be tested.
XRF instruments are small and light (weighing less than 2 kg). A single measurement takes about 5 s. Little is required by way of sample preparation. Grinding is usually unnecessary.
However, only elements present in amounts of more than 0.5% can be reliably determined with X-ray fluorescence. These systems cannot be used to determine the light elements C, P, S and Mg in an iron base.
Arc OES instruments are available as small and lightweight systems. Measurements can often be made without having to grind the workpiece. Single measurement times of 3 s are usual.
Most relevant elements can be determined with sufficient accuracy.
Many chemical elements can be identified and quantitatively determined with arc spectrometers.
However, carbon cannot be determined with the necessary accuracy because atmospheric carbon dioxide gives a strong background signal. The CO2 content of ambient air (normally 360 ppm) results in a carbon signal on the carbon line at 193.0 nm which corresponds to the signal for a content of about 0.25% C in steels.
However, carbon in particular has a significant influence on the physical properties of metallic materials, such as steel.
It is therefore an object of the present invention to provide an apparatus and a method for improved C determination.